The present invention relates to a waste gas treating burner for use in a combustion-type waste gas treatment system for combusting harmful waste gases such as a deposition gas containing SiH4 and a halogen-base gas (CHF3, C2F6, CF4, etc.), which are emitted from semiconductor manufacturing system.
Semiconductor manufacturing system emits harmful waste gases such as a deposition gas containing SiH4 and a halogen-base gas (CHF3, C2F6, CF4, etc.), which should not be discharged directly into the atmosphere. It is therefore the general practice in the art to introduce such harmful waste gases into an abatement system where the waste gas is detoxified by way of combustion. According to the general waste gas treatment system, an auxiliary combustible gas is used to produce flames in a furnace for thereby combusting the waste gases.
In the combustion-type waste gas treatment system, the auxiliary combustible gas is usually in the form of a combination of a fuel gas such as hydrogen, a town gas, LPG, etc. and an oxidizing agent such as oxygen or air. Most of the operating cost of the combustion-type waste gas treatment system constitutes expenses required by the consumption of the fuel gas and the oxidizing agent. One of the indicators of the performance of combustion-type waste gas treatment system is how much harmful waste gases can be destroyed with a high efficiency with a small amount of auxiliary combustible gas. It is known in the art that when the deposition gas containing SiH4 is thermally destroyed, a powder of SiO2 is generated which tends to be deposited in the combustion chamber and cause various troubles to the combustion chamber. Consequently, a design approach to make the combustion chamber resistant to the deposition therein of a powder of SiO2 is also an important element in evaluating the combustion-type waste gas treatment system.
One general burner for use in conventional combustion-type waste gas treatment system is shown in FIGS. 28 and 29 of the accompanying drawings. As shown in FIGS. 28 and 29, the burner has a waste gas nozzle 2 defined centrally in the ceiling of a cylindrical combustion chamber 1, for introducing a waste gas A to be treated into the combustion chamber 1, and a plurality of auxiliary combustible gas nozzles 3 defined in the ceiling of the cylindrical combustion chamber 1 around the waste gas nozzle 2, for introducing an auxiliary combustible gas B into the combustion chamber 1, with a combustion gas outlet 4 integrally joined to the lower end of the combustion chamber 1. The auxiliary combustible gas B ejected from the auxiliary combustible gas nozzles 3 produces flames in a circular pattern. While the waste gas A passes centrally through the circular pattern of flames, the waste gas A is mixed with and combusted by the flames, emitting a combustion exhaust gas which is discharged out of the combustion chamber 1 through the combustion gas outlet 4.
With the conventional burner, however, since the flames produced by the auxiliary combustible gas are formed in front of the auxiliary combustible gas nozzles, the waste gas discharged forward from the waste gas nozzle which is positioned inwardly of the auxiliary combustible gas nozzles is not necessarily sufficiently mixed with the flames, and hence the efficiency of destruction of the waste gas is not sufficiently high. In order to increase the efficiency of destruction, it is necessary to increase the amount of auxiliary combustible gas to produce large flames, which allow the waste gas to be easily combusted and destroyed. However, the amount of auxiliary combustible gas, which does not contribute to the destruction of the waste gas is also increased, resulting in an increase in the operating cost of the combustion-type waste gas treatment system.
When a SiH4 gas is destroyed by way of oxidization, a produced powder of SiO2 is attached to and deposited on wall surfaces where the exhaust gas flows slowly. If the concentration of SiH4 in the waste gas is high, then the powder of SiO2 is produced and deposited in an increased quantity on the wall surfaces. In worst cases, an auxiliary combustible gas may not be continuously combusted, and it may be necessary to shut off the combustion-type waste gas treatment system for removal of the deposited powder.
The present invention has been made in view of the above difficulties. It is an object of the present invention to provide a burner for use in a combustion-type waste gas treatment system which is capable of destructing waste gases, particularly, a deposition gas containing SiH4 and a halogen-base gas, from a semiconductor fabrication facility simultaneously at a high efficiency of destruction, making it difficult for a powder of SiO2 to be attached and deposited, performing a low-NOx combustion, and maintaining a desired level of safety.
According to the present invention, there is provided a burner for treating a waste gas, characterized in that a flame stabilizing zone is open toward a combustion chamber, surrounded by a peripheral wall, and closed by a plate remotely from the combustion chamber, and a waste gas, an auxiliary combustible agent, and air are introduced into and mixed with each other in the flame stabilizing zone, and the mixed gases are ejected toward the combustion chamber perpendicularly to the plate. Preferably, the plate has, defined therein, a waste gas flame hole for ejecting the waste gas toward the flame stabilizing zone and an auxiliary combustible gas flame hole for ejecting the auxiliary combustible gas, and the peripheral wall of the flame stabilizing zone has an air ejection nozzle arranged to eject the air substantially circumferentially to produce a swirling flow.
The waste gas including a deposition gas and a halogen-base gas, the auxiliary combustible agent, and the air are introduced into the flame stabilizing zone, which is open toward the combustion chamber, and sufficiently mixed with each other. The mixed gases remain sufficiently mixed without being dispersed, and are ejected toward the combustion chamber perpendicularly to the plate. Combustion flames produced in the combustion chamber become elongate flames, expanding a high-temperature region downstream to increase the period of time in which the waste gas remains in the high-temperature region. Therefore, the waste gas is well combusted with a high efficiency of destruction, and a powder of SiO2, which is produced, is efficiently discharged by a flow of combustion gas.
The air ejected substantially circumferentially from the peripheral wall produces a strong swirling flow. The swirling flow has a vortex center of the swirling air and a free vortex region around the vortex center. Since the flame holes for the waste gas and the auxiliary combustible gas are defined in the plate, the waste gas and the auxiliary combustible gas which are ejected from the flame holes are introduced into the free vortex region and engulfed by the swirling air flow. The waste gas and the auxiliary combustible gas, which are ejected from the flame holes, are sheared due to changed in the speed of the swirling air flow by the free vortex region of the swirling air flow, and sufficiently mixed with the air, and the mixture of the waste gas, the auxiliary combustible gas, and the air produces swirling flames. Because the auxiliary combustible gas and the air are combusted after being mixed in the swirling air flow, they produce pre-mixed flames to achieve a low-NOx combustion. Since the auxiliary combustible agent and the air are mixed in the flame stabilizing zone, the auxiliary combustible agent is not ignited in the gas chamber, making the burner highly safe, even when the peripheral wall of the flame stabilizing zone is heated by the flames.
Preferably, a second auxiliary combustible gas flame hole for ejecting the auxiliary combustible gas is defined in the peripheral wall of the flame stabilizing zone downstream of the air ejection nozzle in an axial direction of the flame stabilizing zone.
Flames produced by the auxiliary combustible gas are positioned downstream of the second auxiliary combustible gas flame hole, and are combined flames from the primary combustion, producing elongate flames. The elongate flames expand a high-temperature region downstream to increase the period of time in which the waste gas remains in the high-temperature region. By thus expanding the flame-induced high-temperature region downstream, the halogen-base waste gas in particular can fully be destroyed.
The air ejection nozzle preferably comprises air ejection nozzles in a plurality of groups divided along the axial direction of the flame stabilizing zone.
When the air is divided in a plurality of groups and supplied to the flame stabilizing zone, the amount of air ejected from each of the groups is small. At the inlet of the flame stabilizing zone, the amount of air required to combust the auxiliary combustible gas is insufficient, producing fuel-rich flames, suppressing the generation of NOx. At the outlet of the flame stabilizing zone, a sufficient amount of air is supplied to produce fuel-lean flames, causing a low-NOx combustion. Flames produced by the air ejected from the air ejection nozzles in the plural groups become elongate flames. The elongate flames expand a high-temperature region downstream to increase the period of time in which the waste gas remains in the high-temperature region, thus fully destructing the halogen-base waste gas in particular.
The flame stabilizing zone preferably is of a cylindrical shape. If an air ejection nozzle for ejecting air substantially circumferentially is combined with the flame stabilizing zone, then a swirling air flow can easily be produced in the flame stabilizing zone.
In a burner according to a second aspect of the present invention, a second flame stabilizing zone is disposed downstream in the axial direction of the flame stabilizing zone, and has, defined in a peripheral wall thereof, a second auxiliary combustible gas flame hole for ejecting a second auxiliary combustible gas, and a combustion chamber is disposed downstream of the second auxiliary combustible gas flame hole in an axial direction of the second flame stabilizing zone.
With the above arrangement, primary pre-mixed fuel-lean flames are produced downstream of the flame stabilizing zone, and then the auxiliary combustible gas is ejected from the second flame stabilizing zone to produce secondary high-temperature low-oxygen flames downstream thereof. Therefore, a deposition gas containing SiH4 and a halogen-base gas can simultaneously be destroyed with a high efficiency, and a powder of SiO2, which is produced, can efficiently be discharged by a flow of combustion gas. Consequently, the powder of SiO2 is prevented from being deposited in the combustion chamber.